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HVAC Discussions - Heating, ventilation and air conditioning.
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Posted by Tony on April 14, 2007, 6:22 pm
Bill
I am not HVAC person however I am refrigeration mechanic or
tech. whatever you wish to apply, if you think that you are puzzel
by SEER formula let me gave you something ales to think about
Must of us supose to know OHMS LAW at least I think so,
lets take your problem for example at round off numbers
Voltage is 220
your total Curent is 18.
18 x 220= 3960 watts
according to formula 1 watt=3.412 Btus
3960 watts x 3.412= 13,511 Btus
yet your AC is rated at 36,000 Btus
your Ac puts out 22,489 Btus more then is taking in.
So your AC is Apx 266% efficent.
That is called energy saving! WOOooooo
Hello I am not aducated am'I confused? hell yes and in
my opinion person who came up with this formulas
must have few beers or did it purposly so that must
of us can not come out with proper answer do I need
education yes but I would still say the person that came
up with this system was stupid arrogant idiot.
Dido
> I'm hoping I can get an explanation about SEER that makes sense.
> Here's
> my situation. I am going to have a Trane XL19i compressor added to
> my
> existing Trane XV90 heating system (the brand and particulars don't
> really
> matter...). I am going to have the HVAC work done by a pro, but I
> want
> to run the electric myself. I am trying to understand the electric
> load in
> some detail and it just doesn't add up.
>
> I am considering a 36kBTU (3 ton) compressor. The spec sheet says
> that it needs a 30A 220V dedicated circuit (which is fine...), but I
> am
> trying to figure out what the *true* load on the subpanel will be.
> The spec
> sheet says that the max compressor draw is 15.1A and that the max fan
> draw is 2.8A. So, I figure that when the unit is running wide open
> it
> can be drawing 17.9A.
>
> Here's my confusion. 36000BTU/19SEER = 1895watts. At 220V this
> implies 8.6A. What's up with this?
>
> I came up with a number of possibilities:
> *the 15.1A on the compressor load is the inrush current at startup
> *the compressor never runs at 100% duty cycle (this makes no sense to
> me).
>
> What I want to know is when the compressor and fan are already
> running
> (that is neglecting any startup transients) how much current will this
> unit
> (compressor plus fan) be drawing from my subpanel.
>
> Any help much appreciated.
>
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Posted by Sparks Johanson on April 15, 2007, 3:15 am
>3960 watts x 3.412= 13,511 Btus
>yet your AC is rated at 36,000 Btus
>your Ac puts out 22,489 Btus more then is taking in.
>So your AC is Apx 266% efficent.
>That is called energy saving! WOOooooo
Not quite. That means that your AC uses 3960 watts (13511btu) to move
36000 Btu's from here to there. This gives you an EER of 36000/3960 of
about 9.1. Or, you could say that for every watt of electricity is
consumes, it moves 2.66 watts out of the conditioned space. That's not
the same thing at 266% efficient. It does, however, mean that (if you
had a heat pump) you could move at least 2.66 watts into the space for
every watt of energy you consume. Recall, furnaces that burn fuel
cannot provide more that 1 watt of heat per watt of energy consumed,
i.e, their efficiency is < 1 (Say 80 or 90%.)
Lesson? It's often cheaper to move heat around than to create it.
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Posted by Tony on April 15, 2007, 11:13 am
>
>
>>3960 watts x 3.412= 13,511 Btus
>>yet your AC is rated at 36,000 Btus
>>your Ac puts out 22,489 Btus more then is taking in.
>>So your AC is Apx 266% efficent.
>>That is called energy saving! WOOooooo
>
> Not quite. That means that your AC uses 3960 watts (13511btu) to move
> 36000 Btu's from here to there. This gives you an EER of 36000/3960 of
> about 9.1. Or, you could say that for every watt of electricity is
> consumes, it moves 2.66 watts out of the conditioned space. That's not
> the same thing at 266% efficient. It does, however, mean that (if you
> had a heat pump) you could move at least 2.66 watts into the space for
> every watt of energy you consume. Recall, furnaces that burn fuel
> cannot provide more that 1 watt of heat per watt of energy consumed,
> i.e, their efficiency is < 1 (Say 80 or 90%.)
>
> Lesson? It's often cheaper to move heat around than to create it.
Mr. S. Johanson
You are right and I understand what are you saying.
what I am saying that formula at very beginning
it was not design the way I see it as should have been
as you stated for every watt of electricity is consumed
it moves apx.2.66 watts out of conditioning space
that you may say that you take volts wagon to
move car carrier, or taking step up transformer 50 volt @ 2amp.
to generate 100 volt and 1 amp. is not going to happen
I am sorry but AC formulas that is in use to me do not compute.
any time you are changing energy from one to another
they are loses it doesn't matter how change or conversions
take it's place, how efficient change is they are loses.
My point is that our predecessors have screwed up.
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Posted by Sparks Johanson on April 17, 2007, 12:53 am
>You are right and I understand what are you saying.
>what I am saying that formula at very beginning
>it was not design the way I see it as should have been
>as you stated for every watt of electricity is consumed
>it moves apx.2.66 watts out of conditioning space
>that you may say that you take volts wagon to
>move car carrier, or taking step up transformer 50 volt @ 2amp.
>to generate 100 volt and 1 amp. is not going to happen
>I am sorry but AC formulas that is in use to me do not compute.
Well, think about it this way. Your air conditioner is doing work by
moving stuff from here to there. Don't worry about the stuff, for the
moment. Now, how efficiently can it do that? Certainly, less that
100%, as no machine can do work 100% efficiently. How inefficient is
it? An ideal air conditioner would have a Coefficient of Performance
of about 8 or 9, depending on the precise conditions. This is known as
the Carnot efficiency, and is the very best you can do, with a
perfectly efficient machine. (This is calculated by Tevap/(Tcond -
Tevap) where T's are in Kelvin)
So, your air conditioner, with a COP of 2.66, is actually about 2.66/8
= 33% efficient. Not that great.
I don't quite understand your point with the volts wagon and the car
carrier.
>any time you are changing energy from one to another
>they are loses it doesn't matter how change or conversions
>take it's place, how efficient change is they are loses.
Note, that your AC doesn't "put out" BTUs, it simply moves them from
one place to another. Carnot says that to move the 36,000 BTUs to the
outside will require about 4500 Btus of energy input. Yours is
actually using 13,511.
Let's look at it from another perspective. How much energy does it
take to move a container with 2.6 gallons of gas up a hill? (Depends,
of course, on a lot of factors.) Let's say it takes 1 gallon. Would
you say that because I put 1 gallon into the truck, and ended up at
the top of the hill with the 2.6 gallons that my truck is 266%
efficient? Certainly not! Yet, this is essentially what you are doing
if you say that an air conditioner is 266% efficient because it can
move 2.66 Btus for every Btu's worth of electricity.
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